View Full Version : Fin Size Vs. Weight
23rd January 2010, 12:30 PM
Sorry for such a basic question, but shouldn't smaller sailors use smaller fins for a given sail and board when completely powered up? Is there a formula or chart somewhere? If a published recommended fin range for a board is 34 to 42 cm, should I, at 57 kg, expect to use a range of 32 to 40 cm for the published sail size range?
23rd January 2010, 04:43 PM
What board and sail are you using? What wind strength?
At 54kgs, I'm in the same boat. I use a 29cm fin on my 106l board (one for which you would expect a fin more around the size of 33) and now with the footstraps fully back I never get excessive lift, only occasional spinout in chop. Using mainly a 6.0m and 5.3m this works fine for me.
I've also sailed on a 130l Bic with a 36cm fin with 6.0m well powered up and this was unmanageable. Even with both feet in the straps and good form the board would simply lift up too much and become extremely unstable...
In the past I've tried one different fin on my 106l in light winds, a 34cm Tabou freeride fin I believe, and it felt like I was dragging a plastic bag around. I much prefer sacrificing some upwind angle for additional control at speed and less drag with a smaller fin.
Hope this helps.
24th January 2010, 12:45 AM
Not exactly what I was looking for...I probably didn't explain myself very well.
Each board Star-board sells has a recommended sail range and fin range. Does this mean that they would expect that, for the average sailor, one would probably want the smallest fin in the range for the smallest sail in the range, and the biggest fin in the range for the biggest sail?
Then, for a 57 kg sailor, should I reduce those fin size guesses by a few cm across the board? On top of it all, I'll be using weed fins, so I may have to make another size adjustment.
I don't have tons of $$$ to throw at fins. I want to make the most educated guesses as possible.
24th January 2010, 05:08 AM
Yes, smaller, lighterweight sailors can use smaller fins and smaller sails for a given windspeed than larger heavier sailors, but even big sailors tend to use the smallest fin that works for the conditions.
Using a larger fin just adds more drag.
Since you will be using weed fins, and Starboard really gives you no size range applicable to weed fins (they tend to have alot more area than a similar depth (span) vertical race or pointer fin.
What boards are you looking at, and what sail sizes do you think you will be using.
Also some indication about the windspeeds you plan to sail in.
At 57 Kg. I don't think you will be using fins much smaller that those recommended in the range for each Starboard board, and if you will be using weed fins exclusively, there are many different types of weed fins, and some can be sailed very small, others you need a little more size.
What weed fin brands are available in your area?
Hope this helps,
24th January 2010, 08:11 AM
So, what exactly does the published fin range mean?
I'm having a little trouble with the physics that would let a 100kg sailor require the same fin and get the same performance as 57 kg sailor with a given board and sail. (Of course the 100kg sailor will need more wind to be fully powered with that board and sail.) But you've been doing this WAY longer than I have.
24th January 2010, 11:57 AM
Well generally the fin range indicated is linked quite closely to the sail range, ie. smallest fin recommended will probably be about right for the smallest sail recommended.
I'm guessing that a heavier sailor sailing a 6.5m well powered up, for instance, will probably need a bigger fin than a lighter sailing a 6.5m well powered up as for the lighter sailer the leverage of his weight on the rig will be much less significant and therefore so will the sideways forces on the board and he won't need as big a fin.
I guess this is sort of like me taking a 29cm fin with a 6.0m when most sailors would need something bigger.
24th January 2010, 12:29 PM
The "published" fin range is the range of fins that one would normally use in this board
based on an average 80 Kg. sailor.
The "published" range is arrived at based on the width of the board, and alot of testing to see what is too much and what size is too small (again for an average 80 Kg. sailor).
The test team does include both heavier and lighter sailors than the 80 kg. so it's a fair
Since you are much lighter, as agrelon suggests, you can go with a smaller fin for a given sail size, but fin size is always "speculative" in that if you are a bit underpowered you can help the situation with a larger span (length) fin to get you planing sooner, and conversely you can use a smaller fin when overpowered and the board is beginning to get hard to control to get some control back and keep on sailing.
Normally if you are overpowered, it's good to change to both a smaller fin and smaller sail size.
At 57 Kg. you do not fit in the "average 80-85 Kg." sailor category, so the published fin range may not mean very much for someone your size.
Since you are trying to buy fins, it might be a good idea to purchase a fin in the stock size for 2009 and then work up and down from there.
The "stock" fin was always slightly smaller than the mid range for the board.
Some sailors used much larger (like 8-10 cm) and many used smaller (like 4-6 cm) depending on sailor weight to some degree, but wind and water conditions to a larger degree.
Hope this helps,
25th January 2010, 04:51 AM
Its a difficult answer to quantify but ;;;
In any given wind speed a heavier sailor will require a bigger sail and consequently bigger fin ? (Easy ???)
But for any given sail size a heavier sailor is going to be a) probably going faster b) using sail in stronger winds (definitely faster) c) probably using sail in rougher conditions ; all points leading to a smaller in.
I use a 7 metre in upto approx 25 mph.In these conditions (on flat water) Because of board speed I can get away (benefit?) with a 32cm fin.
Daughter (much lighter) uses same sail in 15 mph and copes (benefits?) with a 42 cm fin. (On same board too)
General rule to give starting size is x5 +3. (Sail size in metres ; muliply by 5 and then add 3)
(ie for a 7 metre would be 38cm)
But its only a guide.
If you need better upwind; go bigger.
If you need more control; go smaller.
If you are going for Vmax go as small as possible. Probably)
Generally use smallest you can.
Its worth experimenting. A fin change is wy quicker than a sail change and n do job.
25th January 2010, 05:14 PM
Interesting what you say. My understanding was that a lighter rider would need a smaller fin, all other things being equal: wind speed, sea state, sail size, but... Christine le Couturier (French SB team) revealed that she uses the same sail/fin combinations than her 20 Kgs heavier boyfriend, but in lighter conditions.
Also speedseekers manage to use fins significantly smaller that you would expect for their weight and sails. For instance on my lake the speed record was set by a 90 Kgs guy with 8.4 mē and "only" 36 cm fin. The same day I was also having a 36 but with a 7.3 (well overpowered).
To choose a fin I use a slightly different rule: sail size x5.5 in ideal conditions, x5 when overpovered and x6 when underpowered. This combined with some outhaul extends greatly the range of a sail. This works for my weight (68 Kgs) and freeride/freerace, not slalom/speed/competition. Hope this helps.
25th January 2010, 09:30 PM
There is no perfect answer, just a lot of variables.
Light wind - large fin
High wind - small fin
Large sail - large fin
Small sail - small fin
Heavy sailor - large fin
Light sailor - small fin
Wide board - large fin
Narrow board - small fin
Slow board speed - large fin
Fast board speed - small fin
Upwind performance - large fin
Downwind performance - small fin
25th January 2010, 10:14 PM
At 62 kg my experience is that fin size is ralated to sail size much more than your weight,
so for example, if 100kg person is using 6.0 m2 with 32 cm fin - that what you should be
using also, just for you wind speed would be much lower. The 2 other things to consider: custom fins have better wind range and control and for lighter windsurfer, I strongly believe, softer fins will perform better, more responsive when pumping
26th January 2010, 03:32 PM
Finsize is related to board speed.
Just like sail size is related to windspeed.
27th January 2010, 09:23 AM
The way I've been thinking, unregistered is right. When completely powered up on a given board and sail, the heavier sailor will have the potential to go faster than the lighter sailor of the same ability who is also completely powered. (The bigger sailor needs more wind.) If speed was all that the fin 'sensed', then the heavier sailor may get 'overfinned' sooner.
I always thought it was kinda funny relating required fin size to sail size. There seem to be so many factors, so I guess you have to start somewhere. But fins are pretty stupid. They don't know what size sail is on the board. What do they 'feel'? For sure, the lift they generate is proportional to speed through the water. But, don't they also feel a sideways force. A bigger sailor will generate more of a sideways force than a smaller sailor, again, both being fully powered.
Then again, that bigger sailor being out on the rail probably needs more lift. Who knows? I think I'll just 'guess' on my first fin by getting the cheapest used weed fin I can find, and working from there.
Sergio, what are some of the 'softer' weed fins you know of?
27th January 2010, 01:44 PM
Atfirst get we pressure from leewards and the second is the vacuum on the other side.
Two things who make sometimes to much lift. I reduce on my fins the vacuum on the other side and have so only the lift from leewards, I can so use bigger fins,if I want this.
27th January 2010, 07:24 PM
What those of us who have responded really need to know, to make a good recommendation that almost certain to work for you is the width of the board you are looking at to use with this fin, and the range of sail sizes you think you may be using.
Since you are 57 Kg in weight, you can sail a 100 liter board that's < 60 cm wide in even
12 knots with a 6.5-7.0 m2 rig.
For this setup (57 Kg. 6.5 rig <= 60 cm wide board) I would think a 32 cm Lessacher Duo weed fin would be ab out the best you could get.
If the board size decreases and the windspeed increases to above 20 knots, then a 28 cm Lessacher Duo would be my call.
Do not buy a cheap weed fin.... and remember, weed fins have far more area than the fins that are talked about in the speciifcations so you can run probably 20-30% smaller.
The cheap weed fin will most lilkely be slow, give you lots of drag, and very little upwind performance. The Lassacher duos won't have these issues.
Hope this helps,
27th January 2010, 09:40 PM
Sergio, what are some of the 'softer' weed fins you know of?[/QUOTE]
Lanee, I was not referring to weed fins in the reference to 'soft' fin, I generally don't like weed fins, not sure if soft would not apply to them, the only ones that works relatively well ( in my opinion)are Lessacher fins...
While you guys trying to theorize, I spent last 14 years with diff boards and plenty of fins (custom and production) testing what works best fin size wise for me (132lb). So, from experience, the practical way is to match sail size to fin size, sometimes being light weight I have to go even bigger in fin size to avoid spin-outs (comparing to heavier guy).
28th January 2010, 02:29 PM
Hallo Lanee!The bigger sailor need more wind, that is not okay.A bigger hold the sail longer upright, so he makes more speed with the same sail how a not so big sailor.With
the same wind.
Not bigger sailor need more lift, heavier sailor need more lift.
But fins are pretty stupid. I worked out,35 points what a fin should can do. I give all
points in my fins, please no spin out. No problem when the fin is to long and so on....
They feel no sideway force. I worked the concaves so that they make more lift with
slow speed and with high speed is the lift reduced, so no problem with longer fins.
The Formulas need the bending of the fin to produce lift. The lift is there vertical.The soft fin is better to go earlier to plane, through the bending of the fin get you the most
time with speed the problems. I reduce the problems that a fin can make. Carbon fins
are in 100% carbon. No spin outs, fast and make fun. A fin is not pretty stupid.
31st January 2010, 05:29 AM
sail size X5 + 3 = fin size
so 4.0 sail..... multiply times 5 = 20 + 3 = 23cm fin
there are several "in the ball park" formulas for fin selection, since windsurfing is not a math type science , thats all these math type formulas will do, I noticed Roger stated
80KG , I have seen that 75KG is the average weight when referring to fin size, board liter float on..on Being 57KG (eat more cheeseburgers) ;) using my above posted formula I would look at 20-- 21cm .
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